Resin Casting Volume Calculator
Mixing too little resin leaves a half-filled mold and a wasted pour; mixing too much wastes expensive material. The fix is to compute the mold volume before you mix. This calculator handles a rectangular mold (length by width by depth) and converts the result to US fluid ounces and milliliters using the exact gallon and ounce definitions. It then adds your waste allowance, splits the total by your resin-to-hardener mix ratio, and optionally converts to weight if you enter your resin's density. The mix ratio and density come from your product's data sheet, so nothing is assumed.
Resin volume formula
Mold volume (cu in) = length * width * depth
With waste = mold volume * (1 + waste% / 100)
Fluid ounces = cu in * 128 / 231
Milliliters = fl oz * 29.5735
Resin mL = total mL * resin / (resin + hardener)
Hardener mL = total mL * hardener / (resin + hardener)
One US gallon is 231 cubic inches and 128 fluid ounces; one fluid ounce is 29.5735 mL. These exact conversions come from the NIST Office of Weights and Measures.
Resin casting context
- One cubic inch equals about 0.5541 US fluid ounces (128 / 231).
- Mix epoxy precisely at the ratio on the product label; off-ratio mixes may not fully cure.
- A waste allowance of 5 to 10 percent covers resin left in the cup and on the stir stick.
- For deep pours, follow the maximum pour depth on the product data sheet to avoid overheating.
- Volume and unit definitions follow the NIST Office of Weights and Measures.
Resin volume: frequently asked questions
How do I calculate resin volume for a mold?
For a rectangular mold, multiply length by width by depth. For a cylindrical mold, multiply pi by radius squared by depth. That gives the volume in cubic inches, which the calculator converts to fluid ounces and milliliters. Mix a little extra to cover the meniscus and any residue left in the cup.
How do fluid ounces relate to cubic inches?
One US gallon is exactly 231 cubic inches and contains 128 US fluid ounces, so one cubic inch equals 128 divided by 231, about 0.5541 fluid ounces. One US fluid ounce is exactly 29.5735 milliliters. The calculator applies these exact conversions defined by the NIST Office of Weights and Measures.
How does the mix ratio work?
Epoxy resin is mixed by volume or weight in a ratio such as 1 to 1 or 2 to 1 (resin to hardener). Enter your ratio and the calculator splits the total volume into the two parts. Always follow your product's stated ratio precisely, because an off-ratio mix may not cure.
Should I add extra resin?
Yes. Some resin clings to the mixing cup and stir stick, and you want the mold filled to or slightly above the rim. A waste allowance of around 5 to 10 percent is common. Enter your own allowance; the calculator adds it to the mold volume to give the amount to mix.
Does this give weight or volume?
It gives volume by default, which is how many resin systems are measured. If your resin specifies a weight ratio, enter its density to convert volume to grams. Density varies by product, so it is a user input; check your resin's technical data sheet for the figure.
Official sources
- NIST: Units of volume (gallon and fluid ounce).
- NIST: Office of Weights and Measures.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.